Systemic Inflammatory Response Syndrome (SIRS) is a condition associated with a systemic inflammatory response to an infection. SIRS can occur in patients with sterile inflammation processes (for example, pancreatitis, multiple trauma, ischemia, etc.) or with bacterial infections. SIRS is commonly diagnosed when two or more of the following symptoms are present: body temperature less than 36° C. or greater than 38° C., heart rate greater than 90 beats per minute, respiratory rate of more than 20 breaths per minute or atrial carbon dioxide tension of less than 32 mm Hg, and a white blood cell count of greater than 12,000 μL or less than 4,000/μL or 10% immature forms. Sepsis is a subtype of SIRS and is commonly diagnosed when a patient has SIRS in combination with a bacterial infection. Septic shock is a condition that results from uncontrolled sepsis and is commonly diagnosed when a sepsis patient develops refractory hypotension. In order to properly treat the patient, it is important to differentiate between critically ill patients with sterile inflammation and critically ill patients with a bacterial infection. As a general example, antibiotics would not be beneficial to patients with sterile inflammation (SIRS), but may benefit patients with bacterial infection (sepsis/septic shock).
Differentiating between sterile inflammation and bacterial infection in critically ill patients with fever and other signs of the systemic inflammatory response syndrome (SIRS) is an important clinical challenge (Tang, et al. The Lancet Infectious Diseases 7:210-7 (2007); Sutherland, et al. Crit. Care 15:R149 (2011); Tang, et al. Am. J. Resp. Crit. Care Med. 176:676-84 (2007)). While conventional microbiology culture techniques are the standard methodology for such differentiation, these techniques can lack sensitivity. In addition, there is often a substantial delay between obtaining cultures and generating clinically useful data.